Unfortunately, many people equate natural and safe. Thus, this may explain in part the current popularity of products containing
"all natural" active ingredients. However, some of the most toxic compounds known to man are naturally-occurring (botulism,
cyanogenic glycosides, ricin). This presentation will discuss several toxins (poisonous substances occurring naturally) that
represent potential hazards to companion animals. They are chemically diverse and affect a variety of organ systems. In
several cases, the toxin or toxins responsible for tissue damage have not been identified.
Mycotoxins
Vomitoxin or deoxynivalenol has been found in dog foods containing corn, wheat, barley or oats contaminated with toxin-producing
Fusarium spp. molds. Clinical signs in affected animals include sudden onset of feed refusal and emesis. In experimental feeding
trials with dogs, feed refusal has occurred at vomitoxin concentrations of ~ 4 to 5 ppm. Differential diagnosis includes
other causes for anorexia and emesis (viral, bacterial or parasitic), which are very non-specific signs. There are no specific
clinical pathologic or post-mortem findings. Exposure is confirmed by analysis of suspect feed; most veterinary diagnostic
laboratories offer vomitoxin analysis. Treatment involves removal from suspect feed and symptomatic and supportive care.
The prognosis is excellent.
Several Penicillium spp. of molds produce penitrem A and/or roquefortine. Penitrem A poisoning has been reported in dogs that have ingested
moldy food items (moldy cheese, bread or English walnuts). Roquefortine poisoning has been documented in dogs ingesting such
moldy material as dairy products or compost. The mechanism of toxicity is not known, but penitrem A may act by interfering
with central inhibitory neurons or influencing presynpatic transmitter release. Clinical signs include early restlessness,
panting, and hypersalivation followed by mild to moderate whole body muscle tremors. At high doses, tremors can be severe
and seizures may occur. Affected animals may be hyperesthetic. Secondary signs include hyperthermia, exhaustion, dehydration,
metabolic acidosis and rhabdomyolysis. Diagnosis can be confirmed by analysis of vomitus, gastric lavage washings or stomach
contents. Treatment is directed toward appropriate gastrointestinal decontamination procedures and symptomatic and supportive
care. Diazepam is recommended for initially controlling agitation, muscle tremors, or seizures. If unsuccessful, methocarbamol
may be tried. The majority of patients recover within 24 to 48 hours with appropriate care. Differential diagnoses includes
strychnine, metaldehyde, methylxanthines, pyrethrins/pyrethroids, organophosphates/carbamates and eclampsia in pregnant animals.
Zootoxins
Spiders
Latrodectus spp. or black widow spiders are globose black spiders with an hour-glass red-orange abdominal pattern. They are widely distributed
in the US. Single bites are potentially fatal especially to sensitive species such as cats. Clinical signs include progressive
muscle fasiciculations, severe pain, muscle cramping, abdominal rigidity without tenderness, restlessness, hypertension, bronchorrhea,
regional numbness and hypersalivation. The venom of black widow spiders contains several biologically active proteins one
of which, α-latrotoxin, induces neurotransmitter release from nerve terminals. Acetylcholine, noradrenaline, dopamine, glutamate
and enkephalin systems are all affected. There are no confirmatory tests that are available. One clue in cats: they may
vomit up the spider. Early identification of bites is difficult unless the bite is actually witnessed. Treatment includes
the administration of a specific antivenin (Lyovac®, equine origin from Merck) by slow i.v. infusion. Allergic and anaphylactic
reactions can occur. If antivenin is not available, 10% calcium gluconate can be used to help alleviate muscle cramping and
pain.
Loxosceles spp. also inhabit many areas of the US. They have a violin-shaped marking on the dorsum of the cephalothorax. A single
bite is potentially lethal. The site of the bite can be difficult to detect initially. However, a severe dermonecrotic lesion
characterized by erythema, bulla formation, sloughing and scabbing often results. Severe systemic signs are uncommon. A
number of biologically active components of the venom have been identified including hyaluronidase, esterase, alkaline phosphatase,
lipase, 5'-ribonucleotide phosphorylase and sphingomyelinase D. There is no specific antidote available. Case management
is directed toward treating the local cutaneous reaction and systemic manifestations. Dapsone, a leucocyte inhibitor, has
shown efficacy in treating dermal lesions in animal models. Anti-inflammatory, antipyretic and analgesic agents can be useful
although use of agents that potentially interfere with normal clotting should be avoided.
